Many manufacturers of hand-held medical diagnostic instrument products including otoscopes, ophthalmoscopes, et al., such as those from Heine Inc., Welch Allyn, Inc., and Keeler Instruments, among others, have long since utilized miniature incandescent lamps, such as halogen and xenon lamps, as illumination sources. These lamps are typically provided within the handle or the head of the instrument and utilize fiber optic bundles or other optical means to transmit the light from the miniature lamp to the tip opening of the diagnostic instrument, such as an ophthalmoscope, otoscope, or similar device.
Power sources for these lamps are typically either wall mounted or are portable, in the form of batteries provided in the instrument handle and having a nominal voltage of approximately 2.5 or 3.5 volts. These voltages are convenient values, since they match both a stacked arrangement of two or three Nickel cadmium batteries and 3.5 volts in particular is favored since it is also the voltage of a single lithium ion cell. Examples of instruments having same are described, for example, in U.S. Pat. Nos. 4,012,686, 5,559,422, 5,177,424, and 5,542,904.
More recently, there has been considerable interest in the field in light emitting diodes (LEDs) as a potential substitute for miniature incandescent lamps. White versions of these LEDs, such as those described, for example, in U.S. Pat. Nos. 6,069,440 and 5,998,925, among others, the entire contents of which are herein incorporated by reference, provide better illumination capability than predecessor LEDs and are therefore coveted for a myriad of applications due to their longer life, resistance to shock and impact loads, cooler operating temperatures and alternative spectral content as compared with the afore mentioned miniature incandescent lamps. Moreover and adding LEDs in general, such as color LEDs, provide additional benefits such as spectral tuning, IR, spectrally specific illumination, and the like.
It is a general desire in the field that future product improvements incorporating white LEDs as illumination sources be compatible with both the mechanical and electrical features of existing power supplies to which these instruments are interconnected. There are, however, a number of significant differences which must be recognized in the incorporation of the above illumination devices into any previously known medical diagnostic instrument. For example, white LEDs, such as those described above, experience a large variation in forward voltage as compared with miniature incandescent lamps, as well as significant differences in current versus light output and color characteristics. There are also mechanical issues relating to the incorporation of any adapter into a medical diagnostic instrument.
In summary, there is a need to develop an adaptive means which can be mechanically, optically and electrically incorporated into the design of a hand-held medical diagnostic instrument so as to permit an instrument having LEDs as an illumination source to be readily used with a variety of existing power supplies and charging apparatus. There is an additional need to enable current instrument heads which formerly used miniature incandescent lamps to utilize white or color LEDs with these existing power sources.